In the medical field, therapeutic or medicinal liquids are often administered to a patient by an infusion system. There are various types of infusion systems for delivering liquids to a catheter or needle. For example, in one system the liquid is typically contained in a reservoir (a bag or a bottle) suspended above the patient, and delivered through a tube, by the force of gravity. Alternatively, the liquid may be delivered from a reservoir by an infusion pump.
It is sometimes necessary to control the flow rate at which the liquid is delivered to the patient, particularly when the liquid is to be administered continuously over an extended period of time. The flow rate may be varied depending on, for example, the specific medical treatment, type of medicinal or therapeutic agent, or the specific needs of a particular patient. Indeed, a specific patient's need or demand for a particular drug or other agent may vary over time.
A variety of devices and techniques have been devised to control the flow rate at which liquid is delivered. An exemplary device is described in U.S. Pat. No. 5,318,515 for an “Intravenous Flow Regulator Device and Associated Method”, issued to Wilk on Jul. 7, 1994. That device has a freely accessible slider member for selecting a desired the flow rate. Another device is described in U.S. Pat. No. 7,455,072 for a “Device for Selectively Regulating the Flow Rate of a Fluid” to Mabry et al., issued on Nov. 25, 2004. That device has a flow rate selection mechanism that is rotatable between positions.
One difficulty with these devices is the unauthorized or unsupervised adjustments to the flow rate delivered by the device. This problem is addressed by the device described in U.S. Pat. No. 7,455,072 by utilizing an optional security cover and an optional removable key. When such a cover and removable key system is used, there is risk of error in setting the flow rate if the user fails to carefully follow directions or pay attention to the selector position with respect to indicia on the housing or the rotatable selector. For example, the orientation of the key in the device can lead a user to focus on an incorrect portion of the rotatable selector. Matching the incorrect portion of the selector with the desired (i.e., correct) selection position will result in a flow rate that may appear correct but will actually be different from the flow rate indicated by the selection position. Another complication is that a user may not properly align or register the rotatable selector with the selector position that corresponds to the desired flow rate. While the device described in U.S. Pat. No. 7,455,072 may include detent features that provide an audible or haptic response (e.g., an audible “click” or a change in rotational resistance) when the rotatable selector reaches a flow rate setting, the rotatable selector may be left slightly off position or between positions so that it is not fully aligned or registered with the flow rate setting. The result is a flow rate that may appear correct but will actually be different from the flow rate indicated by the selection position.
While the approach described in U.S. Pat. No. 7,455,072 has shown promise, improvements have been sought that would provide more precise selection of fluid flow rates, in a device that is inexpensive to manufacture, and simple and reliable to use.
Thus, there has been a need for a device that allows the selection of any of a plurality of discrete flow rates while avoiding the user error of matching the incorrect portion of the selector with the desired (i.e., correct) selection position. There has been a further need for a device in which the rotatable selector is properly aligned or registered with the selected flow rate and which remains stable over time. In addition, such a device should be easy and inexpensive to manufacture, so that it may be economically made as a disposable item, while providing a high degree of reliability in use.